Royal Observatory Research Articles

Editorial: Biographical Memoirs, Volume 69

Editorial: Biographical Memoirs, Volume 69

References of Halley’s Comet at the Royal Observatory of Cádiz (Spain)

References of Halley’s Comet at the Royal Observatory of Cádiz (Spain)

Congress Mania in Brussels, 1846–1856

In 1853, the director of the Belgium Royal Observatory, Adolphe Quetelet, welcomed delegates from several countries to two consecutive meetings that have acquired considerable reputation as the first international congresses of, respectively, meteorology and statistics. This paper examines the local context where several similar international congresses (on free trade, universal peace, prison reform, public hygiene, etc.) were organized in the same decade. It argues that the new Belgian state developed this new form of international conference in order to bolster its soft power in the Concert of Nations. It also discusses tensions between national interests and global beliefs in the efficiency of science, which arose from these congresses. This essay is part of a special issue entitled Science Diplomacy, edited by Giulia Rispoli and Simone Turchetti.

Proposals to Move the Royal Observatory, Greenwich, 1836–1944

In 1939, the British Admiralty agreed to move the Royal Observatory from Greenwich to a better site away from London. The removal was postponed due to the Second World War, and the observatory’s re-establishment at Herstmonceux Castle in Sussex in the 1940s and 1950s was further delayed by post-war economic difficulties. This paper examines several proposals to remove the observatory that were put forward over a period spanning slightly more than a century before 1939 and asks why none of these were taken up. I argue that the lateness of the move was due partly to astronomers’ fears that the observatory would lose its prestige if moved away from the famous Greenwich meridian and also to certain cultural aspects of professional astronomy in early twentieth-century Britain.

On the Extraction of Microseismic Ground Motion from Analog Seismograms for the Validation of Ocean-Climate Models

AbstractWe report on a pilot demonstration of the usefulness of analog seismograms to improve the database of ocean storms before the 1980s by providing additional data for the quantitative validation of ocean wave modeling, in particular for extreme events. We present a method for automatic digitization of paper seismograms to extract microseismic ground-motion periods and amplitudes. Each minute of the original paper records is scanned and vectorized. The amplitudes are calibrated based on the original metadata taken from official bulletins. The digitized time series is processed to extract power spectral densities, which are compared with modeled microseisms levels computed using a numerical ocean wave model. As a case study, we focus on one month of data recorded at the Royal Observatory of Belgium (ROB) from January to February 1953, around the “Big Flood” event, a tragic storm surge that flooded the lowlands of England, the Netherlands, and Belgium on 1 February 1953. The reconstructed spectrograms for the three components of ground motion show clear storm signatures that we relate to specific sources in the North Atlantic Ocean. However, our models of the Big Flood event based on these data do not result in the expected amplitudes as modeled compared to the observational data when the storm reached its maximum in the southern North Sea. We suggest that the source of microseisms recorded at ROB is related to the primary microseism generated in the North Sea, at periods of 7–8 s. Other discrepancies identified suggest small modifications of the source locations or energy. Reconstructed horizontal and vertical ground motions are coherent. This is a good news for the purpose of present-day analyses of constructing twentieth century ocean-climate models, especially as during much of that time only horizontal seismographs were installed at observatories.

Editorial: Biographical Memoirs , Volume 68

Editorial: <i>Biographical Memoirs</i> , Volume 68

Temporary Measures: Women Computers at the Royal Observatory, Greenwich, 1890–1895

Between 1890 and 1895, five women “computers” were hired to work at the Royal Observatory, Greenwich, one of the world’s leading observatories at the time. Caroline Herschel notwithstanding, these women were the very first in Britain to be paid for astronomical observation. They were hired as supernumerary computers – normally a temporary position reserved for young schoolboys. Instead of adhering to the usual strict regimen of astronomical calculations, the women at Greenwich functioned much more as astronomers. They observed with telescopes, engaged in original research, and even published their findings. This paper examines how exactly this occurred at a time when women remained excluded from professional observation elsewhere. It engages original archival research in combination with the Greenwich published literature to shed light on a little-known story that reveals how women in Britain first came to be paid as professional astronomers.

Constructing the 'automatic' Greenwich time system: George Biddell Airy and the telegraphic distribution of time, c.1852-1880.

In the context of the telegraphic distribution of Greenwich time, while the early experiments, the roles of successive Astronomers Royal in its expansion, and its impacts on the standardization of time in Victorian Britain have all been evaluated, the attempts of George Biddell Airy and his collaborators in constructing the Royal Observatory's time signals as the authoritative source of standard time have been underexplored within the existing historical literature. This paper focuses on the wide-ranging activities of Airy, his assistant astronomers, telegraph engineers, clockmakers and others, which served to increase the reliability of the Royal Observatory's time service between the 1850s and 1870s. Airy and his collaborators aimed to mechanize and automate their telegraphic time distribution system in order to improve its accuracy and reliability. The accomplishment of such technological innovations was disseminated via public lectures, journal articles and correspondence with experts, secondary distributors of standard time and the general public. These communications were used to build public trust in the Greenwich time service. However, the unexplored archival material used in the present paper provides fresh insight into the unstable nature of the Greenwich time system, including its clear limits in terms of its scale of automation and degree of accuracy.

Royal Observatory: always working hard

Royal Observatory: always working hard

Adaptive model predictions of daily total column ozone over the Amazon Inter-Tropical Confluence Zone

The aim of this paper is to broaden the scope of a recent adaptive model in order to obtain predictions of total column ozone (TCO) trends over the Amazon Inter-Tropical Confluence Zone (ITCZ). The adaptive model makes daily TCO predictions over the tropical equator-Andes-Region, relying on seasonal patterns and the solar cycle. This study uses daily observations of the sunspot number cycle, given by the World Data Center for the production, preservation and dissemination of the international sunspot number (Royal Observatory of Belgium), and satellite total-column ozone data, collected by NASA (January 1979 to April 2018), for two Colombian locations: one in and one adjacent to the ITCZ. The agreement between daily total-column predictions by the adaptive model and satellite observations is excellent. Daily averaged relative errors around of 3.7 % and 2.8 % for both locations are reported herein.

NEW ASTROMETRIC REDUCTION OF THE SUPERCOSMOS PLATE ARCHIVE: FIRST RESULTS

The arrivals of the new more accuracy reference catalogues and also development of new meth- ods and approaches for reduction astrometric data give the new life for photographic plates archives. Gaia DR2 is not only a giant step in the astrometric accuracy allowing to measure new objects also provides plates archives ob- served in the past with modern accuracy. In this work we present the first results of astrometric reduction in the sys- tem of Gaia DR2 for some photographic plates that were obtained by UK Schmidt telescope (UKST) and digitized by the SuperCOSMOS scanning machine. The UKST is a classical Schmidt with the following parameters: mirror diameter 1.83m; focal length 3.07m; photographic plate size 356mm square, covering 6.4 x 6.4 degrees of sky; plate scale 67.12 arcsec/mm. To date the UKST has taken over 17,000 plates, the plates are stored in the Plate Li- brary at the Royal Observatory, Edinburgh. The photo- graphic plates are digitized to 15 bits (32768 grey levels) with a resolution of 10 microns (0.67 arcsec)/pixel). Each digitized Schmidt plate has size 32256x32256 pixels and produces about 2 Gbyte pixel data .. We are making new reduction of photographic plates that allowing to provide valuable data for future researches in astrometry as well as in astrophysics. The obtained astrometric and photometric data from photographic plates were compared with same one from modern catalogues.

Tremoring transits: railways, the Royal Observatory and the capitalist challenge to Victorian astronomical science.

Britain's nineteenth-century railway companies traditionally play a central role in histories of the spread of standard Greenwich time. This relationship at once seems to embody a productive relationship between science and capitalism, with regulated time essential to the formation of a disciplined industrial economy. In this narrative, it is not the state, but capitalistic private commerce which fashioned a national time system. However, as this article demonstrates, the collaboration between railway companies and the Royal Greenwich Observatory was far from harmonious. While railways did employ the accurate time the observatory provided, they were also more than happy to compromise the astronomical institution's ability to take the accurate celestial observations that such time depended on. Observing astronomical transits required the use of troughs of mercury to reflect images of stars, but the construction of a railway too near to the observatory threatened to cause vibrations which would make such readings impossible. Through debates over proposed railway lines near the observatory, it becomes clear how important government protection from private interests was to preserving astronomical standards. This article revises our understanding of the role of railway companies in the dissemination of standard time and argues that state intervention was essential to preserving Victorian British astronomical science.

Improved Multi-GNSS PPP Software for Upgrading the DEMETRA Project Time Monitoring Service

The H2020 DEMETRA project provides short latency clock monitoring services to the time users using the Atomium precise point positioning (PPP) software developed by the Royal Observatory of Belgium. In this paper, three recent updates of the current Atomium software are introduced: adding Galileo signals in the PPP computation; the option to constrain the receiver clock; PPP with integer ambiguity resolution. The advantages of these updates are demonstrated: Combining the Galileo and global positioning system (GPS) signals for PPP time transfer will further improve the frequency stability inside the computation batch; PPP with receiver clock constraint is not only used to reduce the short-term noise of the clock measurements but can also be used for some specific applications to a keep continuous clock solution in the computation batch or retrieve correct clock measurements from extremely noisy environments; the integer PPP allows a continuous clock solution, and improves the mid-term and long-term stability of the frequency transfer compared to the current PPP frequency transfer techniques.

Editorial

Editorial

Bringing research back to the Royal Observatory

Abstract Emily Drabek-Maunder appeals for researchers to get involved with a new observing project at Greenwich.

The gravity database for Belgium

AbstractData and metadata products based on intensive terrestrial gravity measurements covering the Belgian territory have been established compliant to the new ISO19115‐1 profile for gravity‐related data. A short historical introduction on gravity measurements on the Belgian territory is presented, starting with the first gravity measurement in 1892. This paper focuses on gravity data acquired after 1971, which marks the adoption of IGSN71 as a reference for the world network by the International Association of Geodesy (IAG). Next to a complete dataset containing all Belgian gravity data, the available gravity data were reduced to the corresponding measurement campaign, enabling determination of specific metadata (e.g. used gravimeter, tide system parameters, time of acquisition, etc.). New gravity and spirit levelling measurements were executed by the Royal Observatory Belgium and the National Geographic Institute (Federal Mapping Agency) to validate the g‐value at the historical reference base station ‘Carte du Ciel’ in Brussels. Taking into account the instrumental errors and the varying ground water content, the retrieved data are validated and approved for use in further research.

Study of Sunspot Penumbra to Umbra Area Ratio Using Kodaikanal White-light Digitised Data

We study the long-term behaviour of sunspot penumbra to umbra area ratio by analyzing the recently digitized Kodaikanal white-light data (1923-2011). We implement an automatic umbra extraction method and compute the ratio over eight solar cycles (Cycles 16-23). Although the average ratio doesn't show any variation with spot latitudes, cycle phases and strengths, it increases from 5.5 to 6 as the sunspot size increases from 100 $\mu$hem to 2000 $\mu$hem. Interestingly, our analysis also reveals that this ratio for smaller sunspots (area $<$ 100 $\mu$hem) does not have any long-term systematic trend which was earlier reported from the Royal Observatory, Greenwich (RGO) photographic results. To verify the same, we apply our automated extraction technique on Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI) continuum images (1996-2010). Results from this data not only confirm our previous findings, but also show the robustness of our analysis method.

'Greenwich near London': the Royal Observatory and its London networks in the seventeenth and eighteenth centuries.

Built in Greenwich in 1675-1676, the Royal Observatory was situated outside the capital but was deeply enmeshed within its knowledge networks and communities of practice. Scholars have tended to focus on the links cultivated by the Astronomers Royal within scholarly communities in England and Europe but the observatory was also deeply reliant on and engaged with London's institutions and practical mathematical community. It was a royal foundation, situated within one government board, taking a leading role on another, and overseen by Visitors selected by the Royal Society of London. These links helped develop institutional continuity, while instrument-makers, assistants and other collaborators, who were often active in the city as mathematical authors and teachers, formed an extended community with interest in the observatory's continued existence. After outlining the often highly contingent institutional and personal connections that shaped and supported the observatory, this article considers the role of two early assistants, James Hodgson and Thomas Weston. By championing John Flamsteed's legacy and sharing observatory knowledge and practice beyond its walls, they ensured awareness of and potential users for its outputs. They and their successors helped to develop a particular, and ultimately influential, approach to astronomical and mathematical practice and teaching.

Twentieth-Century Longitude: When Greenwich Moved

By the beginning of the twentieth century, the meridian passing though the Royal Observatory at Greenwich had become a near-universal reference for place and time. It was the zero of longitude. But our current standard of zero longitude is about 100 metres away from the original. That mobility needs historical context: Greenwich began to move in the years after the First World War, when wireless techniques for the astronomical determination of longitude and the standardisation of time were developed, and has carried on moving ever since. In this article, I describe how twentieth-century techniques for the determination of longitude not only brought improved precision but also led to fundamental changes in our long-standing conventions of longitude. And I show how – despite its mobility – our current standard of zero longitude continues to respect the original.

Prediction of maximum amplitude of solar cycle 25 using machine learning

Prediction of maximum amplitude of Solar Cycle 25 is obtained by using four different machine learning regression methods, i.e. Linear Regression (LR), Random Forest (RF), Radial Basis Function (RBF) and Support Vector Machine (SVM). Monthly mean sunspot number data during the 1856-June 2018 (solar cycles 10-24) from the World Data Center SILSO, Royal Observatory of Belgium, Brussels are used as machine learning inputs. According to LR, RF, RBF and SVM, the maximum of Solar Cycle 25 is predicted to occur in September 2023 (sunspot number of 159.4 ± 22.3), in December 2024 (sunspot number of 110.2 ± 12.8), in December 2024 (sunspot number of 95.5 ± 21.9) and in July 2024 (sunspot number of 93.7 ± 23.2), respectively. The prediction using LR method suggested that Solar Cycle 25 maximum will be slightly higher than the current cycle, while RBF and SVM suggested much lower cycles. RF prediction suggested a lower maximum with well-constructed double-peak. It was also found that the Solar Cycle 25 is predicted to begin in the late 2019 or early 2020 according to all four methods.